Production of ammonium thiocyanate



Patented May 18, 1954 PRODUCTION OF AMMONIUM THIOCYANATE Nelson B. Russell, El Dorado, Ark., assignor to Lion Oil Company, El

tion of Delaware Dorado, Ark., a corpora- No Drawing. Application April 20, 1951, Serial No. 222,161

13 Claims.

This invention relates to a method of preparing ammonium thiocyanate.

By sulfur as used herein is meant elemental sulfur. In View of the fact that an aqueous system is used in this invention, by ammonium sulfide as used herein is meant aqueous ammonium sulfide. By elevated pressure and elevated temperature as used herein is meant pressures above atmospheric and temperatures at or above the boiling point (approximately 40 C.) of the reaction mixture defined hereinafter.

It is known that ammonium thiocyanate can be prepared from hydrocyanic acid, ammonia (as such or as ammonium hydroxide), and sulfur, the sulfur being carried in ammonium sulfide. The major drawback to this process as heretofore practiced is that the rate of reaction is not sufficiently rapid to render the process as feasible as desired commercially. A further serious draw back is that the slow rate of reaction produces a colored product, the depth and extent of the color varying directly with reaction time. A colorless product is desired.

An object of this invention is to provide an improved proces of preparing ammonium thiocyanate. A further object is to provide an improved process of preparing ammonium thiocyanate from hydrocyanic acid, ammonia andsulfur. A still further object is to provide a process of preparing substantially colorless ammonium thiocyanate in which the reaction involved is carried out at a rate much greater than heretofore found possible. Further objects will be apparent from the description of this invention given herein after.

The above objects are accomplished according to this invention broadly by reacting together hydrocyanic acid, ammonia, and sulfur in the presence of ammonium sulfide in which initially in excess of 4.2% and preferably at least about 20 of the sulfur is dissolved. It is specifically preferred that at least about 50% of the sulfur will be initially dissolved in the ammonium sulfide. In order to prevent loss of the reactants (particularly hydrocyanic acid) and a consequent reduction in yieid, preferably the reaction temperature will be held below the boiling point of the reaction mixture, which is about 40 C. Thus preferably the temperature will be held to not exceed about 38 C.

In U. S. Patent 2,293,031, 4.2% is the maximum amount of sulfur shown initially dissolved in the ammonium sulfide.

It has been found according to this invention that the rate of the above reaction varies directly with the per cent of the sulfur initially dissolved in the ammonium sulfide; that as the per cent sulfur initially so dissolved exceeds that of the art (4.2%), the reaction rate shown therein improves; that if at least about 20% of the sulfur is initially so dissolved, the improvement in reaction rate over the art definitely becomes significant; that if at least about 28% of the sulfur is initially so dissolved, a more substantial improvement in reaction rate over the art is obtained; that if at least about 60% of the sulfur is initially so dissolved, the reaction can becarried out substantially instantaneously. Furthermore, almost quantitative yields of ammonium thiocyanate of very high purity are obtained provided the reaction temperature is not permitted to exceed about 38 C. I-leretofore several hours were required to complete this reaction.

The following examples illustrate specific embodiments of this invention. For the sake of simplicity, the data from a number of runs are presented in a single example in Table 1 hereinafter. To facilitate handling, aqueous solutions of the hydrocyanic acid and ammonia were employed. The aqueous solution of hydrocyanic acid was prepared from commercial liquid hydrocyanic acid of 97% purity. Other concentrations of hydrocyanic acid and of ammonia up to and ineluding 100% may be used.

EXAMPLE 1 The hydrocyanic acid was added to a mixture of the ammonia and sulfur, the sulfur being carried in the ammonium sulfide. The amount of the sulfur dissolved in the ammonium sulfide was varied from zero to 100% as shown in Table 1. The rate of addition of hydrocyanic acid was as rapid as would permit control of the temperature (the reaction being strongly exothermic) under the circumstances within the ranges given and with water-bath cooling of the reaction mixture. If desired, the reaction can be carried out still more rapidly than shown in the Table 1 below by more rapidly removing the heat from the reaction mixture. After completion of the addition of hydrocyanic acid, the mixture was boiled until free of sulfide. Next the mixture was filtered to remove solids, principally elemental sulfur precipitated because of the slight excess of sulfur used and also from ammonium sulfide oxidation during boiling. The resulting water-clear filtrate contained ammonium tlnocyanate of about 30% concentration. The ammonium thiocyanate obtained was essentially pure (98 %-99% purity).

Frequently there is no need for reducing the product to solid ammonium thiocyanate because it is used for various applications in solutions of the desired concentrations. However if solid ammonium thiocyanate is desired, this can be readily prepared e. g. by evaporating the solution (filtrate) to a high concentration followed by chilling. Other conventional methods may be used to produce solid ammonium thiocyanate from the solution, e. g. those methods disclosed in U. S.

yields of ammonium thiocyanate because of loss of hydrocyanic acid and ammonia. Of course the pressure is dependent upon the temperature employed and varies directly therewith. The pressure involved is autogenously developed. In addition to requiring pressure equipment, a further disadvantage of using elevated conditions is that a colored roduct results.

Example 2 below illustrates a specific embodi- Patent NO. 2,293,031. F01 instance l nt this invention Except as to elevated u thiocyanate can be Obtained by coohPg the temperature and pressure, the conditions are subabOVe hot filtrate to about. and drymg the stantially the same as those set forth in Exthus precipitated ammonium thiocyanate. V ample A summary of the conditions and results ob- EXAWLE 2 tained in the various runs are given in Table l, 15 wherein P Cent parts areby Weig t a d The ammonia, sulfur and ammonium sulfide wherein the yield of ammonium thiooyariate is were placed in a pressure vessel and heated to based on 100% theoretical of one mol of ammo- 90 C. after which the hydrocyanic acid was nium thiocyanate being produced per mol of hyadded. During the reaction time of one ho the drocyanic acid used. 20 reaction temperature varied within the range Table 1 Mol Ratio Percent of Reaction 15mm. 340s Paiii% first? 3 133335 Riii? (Nnms s N113 HON mS 4 dissolved Min. NrnsoN 0 1.04 1.10 1.0 13.4 0.0 27.0 22.74 0.0 23-27 20 10.0 .0133 1.01 1.10 1.0 8.5 0.0 17.9 14.0 4.2 30-30 01.0 .0134 1.01 1.10 1.0 7.0 0.0 14.73 12.17 4.2 25-35 20hr. 31.0 .0270 1.00 1.10 1.0 10.7 1.5 21.5 17.77 8.1 30-30 10 00.2 .0022 1.01 1.10 1.0 8.8 2.9 18.0 15.17 10.3 20-33 03.0 .107 1.01 1.10 1.0 8.9 4.4 18.0 10. 25 28.6 30-33 15 30.5 .187 1.01 1.15 1.0 11.7 11.7 24.3 20.33 50.0 30-33 95.0 .030 1.03 1.10 1.0 10.0 35.5 20.0 17.07 100.0 30-33 30 07.0 .743 1.87 2.0 1.0 3.7 18.6 17.0 s. 17 100.0 -30 00.4

The above data clearly show the important dis- 75 C.-90 C. and the pressure varied within the covery and crux of this invention, namely: that range -90 p.s. i. the reaction rate is a function of the per Cent A summary of the conditions and results obsulfur initially dissolved in the ammonium sultained are given in Table 2 below, wherein perfide; that the reaction rate varies directly as the cen and parts are by weight and wherein the per cent sulfur initially dissolved in the ammoyield of ammonium thiocyanate is based on 100% nium sulfide; and that the reaction can be cartheoretical of one mol of ammonium thiocyanate ried out substantially instantaneously with sumbeing produced per mol of hydrocyanic acid used. Table 2 Parts40% Parts 20% Parts 48% 41 1 031 1 1 .2123; $233333 Rcimmm 2 Pam's 11 mm Aq.HCN Sinitially ature i Yleld (NH4)2S s 7 v 113 HON $3 dissolved G" Mm. NH4SON| .43 1.30 1.10 1.0 27.5 52.3 43.3 35.8 100 75-00 00 101.1

cient cooling of the re t n xt e- M The yields obtained according to this embodip fi fly, these d Show that asihe p r cent ment are substantially quantitative. The abnorsulfur initially dissolved inthe ammonium sulfide mally high yield (101.1%) in this particular exexceeds that of the art (run 2, 4.2%) the reaction ample is attributed to experimental error. rate shown therein improves; that although an Instead of the procedure followed in the foreimprovement in reaction rate is realized with 8% going examples, hydrogen cyanide gas can be as compared with 4% of the sulfur initially so bubbled into the reaction mixture. Likewise, as dissolved (runs 2 and 4), the improvement is a further alternative, the hydrocyanic acid (or more marked when 20% of the sulfur is initially the hydrogen cyanide gas) and the ammonia can so dissolved; that the improvement in reaction be added simultaneously but separately to the rate is quite substantial with 28% of the sulfur other constituents of the reaction mixture. initially s0 dissolved, and that if at least about As many apparently widely different embodi- 60% of the sulfur is initially so dissolved, the rements of this invention may be made without action can be carried out substantially instantadeparting from the spirit and scope thereof, it neously. is to be understood that the invention is not lim- While it is preferred to practice this invention ited to the specific embodiments thereof except by carrying out the reaction at a temperature as defined i th appended l i below the boiling point (approximately 40 C.) of What is claimed is: the reaction mixture and at atmospheric pres- 1. Process of preparing ammonium thiocyanate sure, it is within the scope of this invention to which comprises reacting together hydrocyarnc use elevated temperatures and pressures. If the acid, ammonia and sulfur in the presence of amreaction is carried out under an elevated temmonium sulfide, initially at least about 20% of perature, it is necessary to use 'a closed system the sulfur being dissolved in the ammonium such 'as a pressure vessel in order to "avoid low 2. Process of preparing ammonium thiocyanate which comprises reacting together at a temperature not in excess of 38 C. hydrocyanic acid, animonia and sulfur in the presence of ammonium sulfide, initially at least about of the sulfur being dissolved in the ammonium sulfide.

3. Process of preparing ammonium thiocyanate which comprises reacting together hydrocyanic acid, ammonia and sulfur in the presence of ammonium sulfide, initially about %60% of the sulfur being dissolved in the ammonium sulfide.

4. Process of preparing ammonium thiocyanate which comprises reacting together at a temperature not in excess of 38 C. hydrocyanic acid, ammonia and sulfur in the presence of ammonium sulfide, initially about 30%-60% of the sulfur being dissolved in the ammonium sulfide.

5. Process of preparing ammonium thiocyanate which comprises the steps of adding hydrooyanic acid to a mixture of ammonia, sulfur ammonium sulfide, the ratio of ammonium sulfide to sulfur being such that initially at least about 20% of the sulfur is dissolved in the ammonium sulfide; heating the resulting mixture until free of sulfide; and finally filtering the resulting mixture.

6. Process of preparing ammonium thiocyanate which comprises the steps of adding hydrocyanic acid to a mixture of ammonia, sulfur and ammonium sulfide, the ratio of ammonium sulfide to sulfur being such that initially about 30 %-60 of the sulfur is dissolved in the ammonium sulfide; heating the resulting mixture until free of sulfide; and finally filtering the resulting mixture.

7. Process of preparing ammonium thiocyanate which comprises the steps of adding hydrocyanic acid to a mixture of ammonia, sulfur and ammonium sulfide, the ratio of ammonium sulfide to sulfur being such that initially at least about 20% of the sulfur is dissolved in the ammonium sulfide; heating the resulting mixture until free of sulfide; filtering the resulting mixture; cooling the filtrate to precipitate the ammonium thiocyanate and drying and recovering same.

8. Process of preparing ammonium thiocyanate which comprises the steps of adding hydrocyanic acid to a mixture of ammonia, sulfur and ammonium sulfide while maintaining the temperature of the reaction at not in excess of 38 0., the ratio of ammonium sulfide to sulfur being such that initially at least about 20% of the sulfur is dissolved in the ammonium sulfide; boiling th resulting mixture until free of sulfide; and finally filtering the resulting mixture.

9. Process of preparing ammonium thiocyanate which comprises the steps of adding hydrocyanic acid to a mixture of ammonia, sulfur and ammonium sulfide while maintaining the temperature of the reaction at not in excess of 38 C., the ratio of ammonium sulfide to sulfur being such that initially about 30%-60% of the sulfur is dissolved in the ammonium sulfide; boiling the resulting mixture until free of sulfide; and finally filtering the resulting mixture.

10. Process of preparing ammonium thiccyanate which comprises the steps of adding hydrocyanic acid to a mixture of ammonia, sulfur and ammonium sulfide while maintaining the temperature of the reaction at not in excess of 38 C., the ratio of ammonium sulfide to sulfur being such that initially about 30%60% of the sulfur is dissolved in the ammonium sulfide; boiling the resulting mixture until free of sulfide; filtering the resulting mixture; cooling the filtrate to precipitate the ammonium thiocyanate and drying and recovering same.

11. Process of preparing ammonium thio cyanate which comprises the steps of adding hy drccyanic acid to a mixture under elevated temperature and pressure of ammonia, sulfur and ammonium sulfide, the ratio of ammonium sulfide to sulfur being such that initially at least about 20% of the sulfur is dissolved in the ammonium sulfide; heating the resulting mixture under atmospheric pressure until free of sulfide; and finally filtering the mixture.

12. Process of preparing ammonium thiocyanate which comprises the steps of adding hydrooyanic acid to a mixture under elevated temperature and pressure of ammonia, sulfur and ammonium sulfide, the ratio of ammonium sulfide to sulfur being such that initially about 30%- 60% of the sulfur is dissolved in the ammonium sulfide; heating the resulting mixture under atmospheric pressure until free of sulfide and finally filtering the mixture.

13. Process of preparing ammonium thicoyanate which comprises the steps of adding hydrocyanic acid to a mixture under elevated temperature and pressure of ammonia, sulfur and ammonium sulfide, the ratio of ammonium sulfid to sulfur being such that initially at least about 20% or" the sulfur is dissolved in the ammonium sulfide; boiling the resulting mixture under atmospheric pressure until free of sulfide; filtering the resulting mixture; cooling the filtrate to precipitate ammonium thiocyanate and drying and recovering same.

References Cited in the file of this patent UNITED STATES PATENTS Numher Name Date 205,152 Smith et a1 July 22, 1902 922,564 Chance May 25, 1909 1,924,206 Hansen Aug. 29, 1933 2,194,438 Wernlund Mar. 19, 1940 2,286,273 Hill Jun 16, 1942 2,293,031 Foster et al Aug. 18, 1942 2,372,119 Riethof Mar. 20, 1945 

1. PROCESS OF PREPARING AMMONIUM THIOCYANATE WHICH COMPRISES REACTING TOGETHER HYDROCYANIC ACID AMMONIA AND SULFUR IN THE PRESENCE OF AMMONIUM SULFIDE, INITIALLY AT LEAST ABOUT 20% OF THE SULFUR BEING DISSOLVED IN THE AMMONIUM SULFIDE. 